Subject: Hot Box Detectors & Generator Exhaust (8/15/00)
The problem is that the generators on PV's are setting off hot box detectors, because of the heat generated by the exhaust. The problem has become more acute because more PV's are running behind box cars, with diesel generators running. Lovett Smith and I talked to the Product Manager of Harmon Industries, makers of hot box detectors, today. He will send me a drawing showing where the detectors are aimed, and a that time I will revise this bulletin.
Generally, a hot box detector has two scanners which point upwardly toward the expected position of the journal, at a 45 degree angle. The particular area of scan is 7" outwardly from the inside head of the rail, and 20" upwardly from the top of the rail. The scanners also read the floor of the car to determine an appropriate ambient temperature. The scanners are not on all the time, instead they are activated only when the wheels are detected. Thus there are transducers which are magnetically switched on by the proximity of the flange of each wheel. Once the wheels pass, the detector is off. The solution appears to be to place the exhaust pipe in a position not seen by the detector, and at a time when the wheels are not activating the detector. Lovett has his exhaust pipe at the level of the side sill, which is beyond the target area of the detector. The Product Manager felt that if the Exhaust Pipe were at least 5' from the nearest wheel, the detector would have switched off before the Pipe got to the Detector. Sound like to me the Exhaust Pipe, if it points outwardly, ought to be up near the side sill, and somewhere toward the middle of the car. A heat shield might help too.
Paul L. DeVerter II
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